The invention relates to an optical moisture sensor, and, more specifically, the invention provides an optical moisture sensor for measuring ambient light conditions.
A focal plane array of photosensors configured as a CCD or CMOS is capable of sensing the presence of rain or other forms of moisture on a vehicle windshield. In general, a lens or reflective optical element is used to form a real image, in the optical sense, of the objects on the focal plane array and that array is then read by addressing each image element or pixel in the array sequentially. The analog output level of each pixel is a function of the integrated light exposure of that image element and is normally converted into a digital value which is stored in the memory buffer. The aggregate of such sequentially addressed and stored digital pixels constitutes an image frame, which can consist of only a few thousand pixels or over a million pixels in high resolution imagers.
In many imaging applications, such as in a conventional television, the stored digital data that forms the image frame is simply read out and is used to create an analog image on a display screen. Other uses for such digitally stored images include metrology and/or machine vision applications where the digitally stored image frame is subjected to image analysis. Still other uses for such digitally stored images include methods whereby stored image frames are analyzed digitally with certain algorithms, in order to recognize the presence of specific characteristic images. Such images might include water drops, rivulets, mist or even dirt.
A problem with optical moisture sensors has been the number of arithmetic computations required to process analog or digital signals generated by the sensing array of the sensor. The sensing array generates a signal based on the conditions it is exposed to. The signal is received by a processor that interprets the signal. When the signal has been interpreted, it can be acted upon. However, interpreting the signal can require the completion of as many as eight billion computations. The processing power required to complete eight billion computations is significant and so the art of optical moisture sensors has been focused on reducing the number of computations required to interpret a signal from a sensing array.
The present invention provides an apparatus and method for measuring ambient light conditions. The present invention adds processing operations to the processor of an optical moisture detector in contravention of the prior art. The invention includes an optical moisture sensor for sensing the presence of moisture on a moisture collecting surface. The sensor is operable to emit a signal corresponding to the sensed conditions. The invention also includes a processor for receiving the signal from the optical moisture sensor, determining a value based on the signal, corresponding to existing ambient light conditions, comparing the value to a predetermined value, and emitting a control signal if the value is less than the predetermined value. Existing processors for optical moisture sensors determine a value based on the signal received from the optical moisture sensor, but do not compare the value to another predetermined value. The predetermined value can correspond to a particular level of ambient light. Specifically, the predetermined value can correspond to a level of ambient light at which the driver of an automobile should engage the headlights of the vehicle. The present invention can also include means responsive to the control signal for controlling a light generating device. For example, the present invention can include a controller for vehicle headlights, the controller operable to receive the control signal from the processor and engage the headlights of a vehicle. The present invention can also include a timer for disengaging the processor from comparing the value to the predetermined value for a period of time. The present invention also can include a processor operable to emit the control signal only if at least two successive comparisons indicate the value corresponding to the level of ambient light is less than the predetermined value. The optical moisture sensor of the present invention can be mounted on the windshield of a vehicle or positioned spaced apart from the windshield. The optical moisture sensor of the present invention can be a CCD camera or a CMOS camera.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.